The present invention relates to a color image forming apparatus in which a plurality of developing units are arranged around the circumferential surface of a photoreceptor, and a color toner image is formed when monocolor toner images are superimposed.
Conventionally, an image forming apparatus is well known, in which a side door of the apparatus is opened for jam clearance and maintenance, and a frame accommodating a photoreceptor and developing units is taken out from the apparatus so as to open a conveyance passage of transfer sheets.
Also, what is called a clam-shell type image forming apparatus is well known, in which an upper and a lower portion of the image forming apparatus are separated from each other for the purpose of jam clearance and maintenance, and a conveyance passage of transfer sheets is opened when the upper portion of the image forming apparatus is opened.
However, when a cartridge accommodating the photoreceptor and developing units is removed from the apparatus main body, there is a possibility that the photoreceptor and developing units are stained when operator's hands are contacted with them. Especially when the image forming body is stained, and also when foreign objects are included in the developing units, the quality of formed images is deteriorated.
In the clam-shell type image forming apparatus, the upper portion is separated from the lower portion with respect to a conveyance line to convey transfer sheets. However, in many cases, the photoreceptor is separated from the transfer unit for the purpose of improving the performance of jam clearance. As a result, most of the circumferential surface of the image forming body, which is usually opposed to the transfer unit, is exposed. Therefore, operator's hands tend to come into contact with the circumferential surface of the image forming body, so that the image forming body is stained.
Further, in the clam-shell type color image forming apparatus, a plurality of developing units are assembled to the upper portion of the apparatus. Accordingly, the weight of the upper portion is increased, and the workability is lowered, and further the mechanical strength, rigidity and balance of the overall apparatus are deteriorated. Therefore, vibration is caused in the process of image formation, so that image quality is deteriorated.